The present invention relates to electrodeposition and, more particularly, to selective removal of a specific metal from a multi-metal plating solution (i.e., a plating solution containing multiple different metals) and, optionally, addition of that specific metal back into the plating solution.
Generally, electrodeposition (also referred to herein as electroplating) is a process in which one or more different metals are deposited onto workpiece using a plating apparatus (also referred to herein as a plating tool). Specifically, in a plating apparatus during electrodeposition, a first electrode comprising a workpiece (i.e., an object, an article, etc.) to be plated and at least one second electrode are placed into a plating solution (i.e., a plating bath) within a plating container (i.e., a reservoir). For purposes of this disclosure, a plating solution comprises at least a solvent (e.g., water) and a substance (e.g., an acid or base) that is dissolved in the solvent and that provides ionic conductivity. The plating solution can comprise one or more organic additive(s) (also referred to herein as organics), such as complexers, charge carriers, levelers, brighteners and/or wetters, dissolved in the solvent. The plating solution can also comprise one or more metal species dissolved in the solvent (see discussion below regarding replenishment of the metal specie(s)). An electrical circuit is created by connecting a negative terminal of a power supply to the first electrode comprising the workpiece to form a cathode and further connecting a positive terminal of the power supply to the second electrode(s) so as to form anode(s). When the electric circuit is created, electric current flows from the anode(s) to the cathode by means of ion transport through the plating solution and electron transfer at the electrodes occurs such that each of the plating materials, which is/are dissolved in the plating solution as a stabilized metal species (i.e., as metal ions), takes up electrons at the cathode, thereby causing a layer of metal or a layer of a metal alloy (e.g., depending upon whether a single or multiple metal species are used) to deposit on the cathode.
The metal specie(s) in the plating solution can be replenished simultaneously by the anode(s), if/when the anode(s) are soluble (i.e., if/when the anode(s) comprise soluble metal(s)) and the electric current used for plating also causes the soluble metal(s) to dissolve in the plating solution). Additionally or alternatively, the metal specie(s) (e.g., in the form of a metal salt or a metal concentrate, which comprises the metal salt previously dissolved in the same solvent as used in the plating solution) as well as any organic additives can be added directly to the plating solution using a plating solution analysis and dosing apparatus (also referred to herein as a plating solution analysis and dosing tool) that is operably connected to the plating apparatus. Specifically, a pair of tubes (referred to herein as slipstream tubes) can provide a continuous path for the transport of plating solution from the plating apparatus to the plating solution analysis and dosing apparatus and back to the plating apparatus. Within the analysis and dosing apparatus the composition of the plating solution is analyzed and, if necessary, the plating solution can be dosed with metal specie(s) and/or organic additive(s) (i.e., metal specie(s) and/or organic additive(s) are added to the plating solution) to achieve the desired composition. As the desired composition is achieved, the plating solution is transported back to the plating apparatus.
While the metal specie(s) in a plating solution can be selectively replenished using the relatively simple techniques described above, selectively removing one or more metal species from a plating solution can be significantly more difficult and/or costly.